Abstract
The relation between the structure and viscoelastic properties of epoxy resins prepared from o-cresol novolacs having different molecular weight distribution was studied. Five kinds of o-cresol novolac were prepared by fractional precipitation of a commerical o-cresol novolac. The fractionated novolacs and commericial novolac were glycidyletherified by epichlorohydrin. These epoxy resins were cured with fournuclei o-cresol novolac as a hardener. Characteristic properties of the cured resins, such as glass transition temperature (Tg), average molecular weight between crosslinking points (Mc), and front facter (φ), were obtained.
The conclusions were as follows : (1) The higher the average molecular weight of a starting novolac, (i) the higher was the Tg, (ii) the larger was the E' in a rubbery region, (iii) the smaller was the Mc, and (iv) the larger was the φ, in the cured epoxy resin. (2) The viscoelastic parameters had a better correlation with the number average molecular weight of a starting novolac than with the weight average molecular weight. (3) The coefficient of linear expansion of a cured epoxy resin was not much influenced by the average molecular weight of a starting novolac.
